The present invention has as its subject a hydraulic section for load sensing applications, and a multiple hydraulic distributor using one or more such hydraulic sections.
A load sensing hydraulic system allows the pressure drop to be maintained substantially constant through a metering orifice of the spool valve of a hydraulic section. As is well-known, a load sensing hydraulic system has application in operating machines which require the simultaneous performance of a plurality of movements. Consider an operating machine with a rotating turret such as, for example, an excavator or a telescopic loader, in which the rotation of the cabin, the extension of the arm and the movement of the bucket are managed independently of each other.
In a load sensing hydraulic system of traditional type, a request for more flow than the maximum deliverable by the pump is followed by the slowing or stoppage of the user with the highest load. This situation would prove particularly critical in the case quoted above, of the operating machine with a rotating turret, because the rotation of the cabin, rather than the extension of the arm, or rather than the movement of the bucket, could stop all of a sudden.
To overcome this problem, distributors of flow-sharing type have been developed, where a request for more flow than the maximum deliverable by the pump is followed by a proportional reduction of the flow to all the users. Although all the users function simultaneously, irrespective of the flow delivered by the pump, there are some applications where the proportional reduction of the flow to some users could compromise the correct operability of the machine. With reference to the operating machine with rotating turret, the speed of rotation of the cabin could undergo numerous oscillations due to the repeated occurrence of conditions of undersupply (or saturation) and restoration of normal conditions of flow, posing considerable problems of control and safety for the operator in the cabin.
It would thus be necessary to make the section corresponding to the critical user (i.e. rotation of the cabin) a priority section with respect to the other sections.
By ‘priority section’ we mean a section which, in conditions of saturation of the flow, does not participate in the proportional reduction of the flow delivered but maintains a constant flow, forcing the other sections to further reduce their flow.
An example of these hybrid solutions is shown in the document GB2271870, which describes a hydraulic system comprising at least one priority section and a plurality of flow-sharing sections. In particular, each flow-sharing section is provided with at least one pressure compensation element and is able to actuate a proportional reduction of flow in case of undersupply (or saturation). In this way, the movement of the machine actuated by means of the priority section does not undergo variations in speed in case of saturation, as happens however with movements whose control is entrusted to the flow-sharing sections. Another similar solution is the one described in the document WO2009/001377.
The main disadvantage of hybrid solutions is connected with the constructional complexity of distributors, which use two types of section with different structures (flow-sharing and priority). In fact, as is clearly visible in document WO2009/001377, the compensation means used in the two types of section are structurally different from each other. This obviously entails longer times and higher costs for design and production than those necessary for the design and production of a load sensing system of traditional type or a load sensing system of flow-sharing type. Add to this the production costs of different moulds for the flow-sharing and priority sections.
Furthermore, hybrid distributors tend to be very bulky because the flow-sharing sections and the priority sections are difficult to accommodate side by side because of the different configurations of the internal channels.
Another problem which can occur in operating machines is that of reverse flow from the workports to the pump feed line which can cause undesired lowering of the load in the initial stage of lifting operations or undesired movements of the users. The expert in the field knows that to eliminate reverse flow, suitably configured non return valves are required, which further complicate the structure of the hydraulic section.
In this context, the technical task at the root of the present invention is to propose a hydraulic section for load sensing applications and a multiple hydraulic distributor which will overcome the disadvantages of the known art cited above.